[Suggestion] Redownload JCEF and CEF on failure to load.

I find that it's a somewhat common issue when downloading or updating some packs that the wrong binary for CEF/JCEF is downloaded, eg before I have crashed due to the windows CEF binary being installed on linux due to the pack developer including the mcef libraries in the pack files. Deleting and redownloading the correct files in the event of the libraries failing to load should fix this issue.